Litigation and Regulatory Matters - Additional Information (Details) $ in Thousands	1 Months Ended							3 Months Ended	12 Months Ended						36 Months Ended
	Jan. 31, 2021 transaction	Jun. 30, 2020 USD ($) financial_institution	Dec. 31, 2019 USD ($)	Sep. 30, 2019 CAD ($)	Mar. 31, 2018 USD ($)	Oct. 31, 2017 formerEmployee	Aug. 31, 2016 formerEmployee	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2014 USD ($) trust	Dec. 31, 2013 USD ($)	Dec. 31, 2012 plaintiff county	Dec. 31, 2007 USD ($)
Loss Contingencies [Line Items]
Expense related to various legal matters									$ 68,000,000	$ 54,000,000	$ 522,000,000
Estimate of reasonably possible loss									150,000,000
Dekalb County et. al. v. HSBC North America Holdings, Inc., et. al. [Member]
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff														3
Number of counties in the area | county														5
Litigation settlement amount			$ 580,000
County of Cook v. HSBC North America Holdings Inc., et. al. [Member]
Loss Contingencies [Line Items]
Litigation settlement amount			580,000
Foreign Exchange Matters [Member] | HSBC Holdings plc [Member]
Loss Contingencies [Line Items]
Number of former employees indicted | formerEmployee							2
Number of former employees found guilty | formerEmployee						1
California Attorney General's Office Investigation [Member]
Loss Contingencies [Line Items]
Litigation settlement amount								$ 7,000,000
FX DPA [Member] | HSBC Holdings plc [Member] | Subsequent Event [Member]
Loss Contingencies [Line Items]
Litigation settlement agreement, compliance period	3 years
Number of transactions investigated | transaction	2
Shareholder Derivative Action [Member]
Loss Contingencies [Line Items]
Deferred prosecution agreement, term												5 years
Insurance settlements receivable from D&O carriers		$ 72,500,000
Supranational, Sovereign and Agency Bonds [Member]
Loss Contingencies [Line Items]
Litigation settlement amount				$ 1,323
South African Competition Tribunal, Revised Complaint [Member]
Loss Contingencies [Line Items]
Number of financial institutions included in complaint | financial_institution		28
Mortgage Securitization Activity Related Litigation [Member] | HSBC Securities [Member]
Loss Contingencies [Line Items]
Mortgage securitization loan purchased and sold															$ 24,000,000,000
Mortgage securitization outstanding loan purchase and sold			$ 3,400,000,000					$ 3,400,000,000	$ 3,100,000,000	$ 3,400,000,000
Deutsche Bank Alleged Breach of Representation [Member]
Loss Contingencies [Line Items]
Damages sought													$ 508,000,000
Mortgage Securitizationn Pool Trust Litigation [Member]
Loss Contingencies [Line Items]
Damages sought												$ 38,000,000,000
Number of identified trusts | trust												280
Rigoberto Vasquez and Eva Garcia et al v. Hong Kong and Shanghai Banking Corporation Ltd., HSBC Bank USA, N.A., et al. [Member]
Loss Contingencies [Line Items]
Damages sought					$ 37,000,000